The present invention relates to counterbalanced arm assemblies, and more particularly to a counterbalanced arm support mechanism for a lamp or the like.
Counterbalanced or equipoised arm assemblies for lamps have been used for many years. The traditional method of counterbalancing an arm support assembly which is pivotally mounted at one end on a mounting bracket and which carries a load at the other end is to fasten one end of a coiled spring to the bracket above the pivoting point and the other end of the spring towards the middle of the arm. This traditional type of arrangement is shown, for example, in U.S. Pat. Nos. 2,787,434; 3,041,060; 3,226,073; 3,543,019; 3,774,873; and 4,080,530.
In counterbalanced arm assemblies of the type shown in the above-mentioned patents, it is generally desirable that the lower arm connected to the support bracket be capable of pivoting or tilting back and forth to an angle of about 60.degree. on either side of the vertical. Prior devices, such as disclosed in the above patents, permit this type of movement while balancing the pivoted arm. As can be seen from the above-noted patents the counterbalancing is achieved with one or more relatively long springs. In double arm constructions, such as shown in the earlier patents, this counterbalancing is traditionally done with one spring on either side of the pivoting arm. However, aesthetic and hygenic requirements often make it desirable to have the spring enclosed within the arm, as is shown in the later patents. However, this confinement of the spring within the arm makes it difficult to obtain proper balancing leverage and torque. With the spring confined, the distance from the pivoting point of the arm to the point on the arm where the spring is connected is restricted, so that the spring has to be both long and heavy in order to produce the necessary counterbalancing force.